Research On Quasicrystals Formation Mechanism By Bond-parameter

Formation mechanism of quasicrystals is a fundamental problem. The formation of quasicrystalline has been effected by many factors. We have studied the effect of size factor and electron factor on the formation of quasicrystalline by bond-parameter method. This quasicrystals include the forth long period transition metals(Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn) based quasicrystals, the fifth long period transition metals (Y,Zr,Nb,Mo,Ru,Rh,Pd,Ag,Cd) based quasicrystals, the sixth long period transition metals (Ha,Ta,W,Re,Os,Ir,Pt,Au) based quasicrystals and the Rare-earth metals (La,Ce,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,E,Yb,Lu) based quasicrystals.The thesis consists of four chapters. In chapter one, we briefly introduce quasicrystals and the formation mechanism of quasicrystals, the theory of bond-parameter method and its application.In chapter two, we have analyzed the effect of size factor and electron factor on the formation of quasicrystals by bond-parameter ellipse model. In this model, the size factor and the electron are expressedas x = R and In a two dimension bond-parametric graph, the alloy elements, which can form quasicrystalline with the based element, can be separated with the alloy elements that can't form quasicrystalline with the based element by anellipse 668 experimental quasicrystals data have been analyzed by this model, which are based on the forty metals. Thereliabilities of this model are up to 93.86%. And the constants m,n,c and d in the ellipse equation can be related to some appropriate parameters of each based metal respectively, namely, m(?)R₀, n(?)y, c(?)(μR₀³)^-(1/2) and d (?) E. Based on this model, we have predicted somepossible new binary quasicrystalsIn chapter three, we have studied the effect of size factor and electron factor on the formation of quasicrystals by bond-parameter parabola model. In this model, the size factor and electron factor aredescribed as and In this model, the alloy elements also can be separated by a parabola y = a-bx². We have analyzed the 668 quasicrystals data by this model. The validity of this model is up to 95.06%. Also, the constants a and b in the parabola equation have been discussed, and these related to some appropriate parameters of based metal, such as, a∝E, b∝EμR₀³. Some new possible quasicrystals have been predicted based on this model.In chapter four a summary of the work and an outlook of this aspect are given.